Not Applicable.
Not Applicable.
The present embodiments relate to communications systems where pilot data is transmitted along with the information data and, more particularly, to channel impulse response estimation in such systems.
In various digital communications environments, the transmitted signal includes information data and, in addition, the transmitted signal includes control data to be used by the receiver for optimizing the communication accuracy between the transmitter and the receiver. One type of such control data is referred to in the art as pilot data, where pilot data is used in the prior art by a receiver to estimate the channel impulse response. This channel estimate is then used to adjust the demodulator of the receiver in an effort to accurately detect the information data. While channel impulse response estimation has been determined using the pilot signal, an improvement on that approach is set forth in U.S. patent application Ser. No. 09/294,722, entitled xe2x80x9cChannel Estimation For Communication System With Pilot Transmission,xe2x80x9d filed Apr. 19, 1999, and hereby incorporated herein by reference (xe2x80x9cthe ""722 applicationxe2x80x9d). In the ""722 application, its inventor achieves an improved channel impulse response estimation at a receiver by determining two estimates, and then combining those estimates to form a single estimate. More specifically, the receiver determines a first channel impulse response estimate based on the pilot data. The approach assumes that the pilot data and information data are transmitted sequentially after each other, that is the information data transmission begins once the pilot data transmission ends and vice versa. Based on that channel response, the receiver makes a preliminary decision on the information data by using, for example, the typical RAKE receiver approach. Once decisions for the information data become available, they can be used to produce a known, constant symbol stream for the information data. This known information symbol stream is then used together with the already known pilot data stream to form a single combined symbol stream which is then used to provide a new channel estimate. Given an acceptable level of accuracy for the preliminary decisions on the information data and the fact that the information data are typically considerably more numerous than the pilot data, the new channel estimate will be more accurate than the initial one which was based solely on the pilot data. Using the new channel estimate, new decisions on the information data are performed. Because of the better accuracy of the new channel estimate, the new information data decisions can also be more accurate. The channel estimation, information data decision process can then be iteratively repeated, using the new, more accurate information data decisions at each step of the iterative process.
While the approach of the ""722 application has been shown to improve upon the prior art approach of using only pilot data to estimate channel impulse response, the present inventor has recognized possible drawbacks of the prior approaches where even greater accuracy is desired. Accordingly, there arises a need to further improve the accuracy of the prior art approaches as is achieved by the preferred embodiment described below. The need to improve the accuracy of the channel estimate using both pilot data and information data has also been examined by S. Min and K. B. Lee in xe2x80x9cPilot and Traffic Based Channel Estimation for DS/CDMA Systemsxe2x80x9d, IEEE, pages 1073-1074, May 1998. In that study, a continuous pilot signal was transmitted in the Q branch of a QPSK signal while the I branch also continuously carried information data. In the present invention, however, and as explored below, the pilot data and information data are transmitted sequentially; that is no pilot data is transmitted when information data is transmitted and vice versa.
In the preferred embodiment, there is a method of operating a communications receiver. The method receives a communications signal which is transmitted via a channel, where the communications signal comprises received known pilot data and received information data, the known pilot data and information data being sequentially transmitted. The method then estimates a first channel impulse response for the channel, wherein the first channel impulse response is in response to the received pilot data. Next, the method determines a group of estimated information data in response to the first channel impulse response. Next, the method estimates a second channel impulse response for the channel in response to the estimated information data. Thereafter, the method forms a combined channel impulse response for the channel. The combined channel impulse response is in response to the estimated information data and the known pilot. The combined channel impulse response is in response to a combination of a first weight applied to the first channel impulse response and a second weight applied to the second channel impulse response, wherein the first weight differs from the second weight. Other circuits, systems, and methods are also disclosed and claimed.